Liquid crystal mask, liquid crystal laser marker, and marking method using the same

ABSTRACT

According to the present invention, no gap occurs in the joint between adjacent blocks when a design is marked in several blocks. In a liquid crystal laser marker for making a liquid crystal mask (2) with a plurality of pixels display a design to be marked on workpieces and for transmitting a laser beam through the liquid crystal mask to a workpiece so that the design will be marked on the workpiece, the liquid crystal mask is such that the pixels at all or part of the outermost sides have a size which is different from that of the inner pixels. The liquid crystal laser marker further includes a controller (11), when a design is divided into several blocks (1, 1, 1) and one of the blocks is displayed on the liquid crystal mask, the controller controls the liquid crystal mask such that a marking position of the block currently displayed on the liquid crystal mask overlaps a marking position of a block adjacent to the currently displayed block by a given length (L 1 , L 2 ) of a portion where the outermost pixels have a size which is different from that of the inner pixels of the liquid crystal mask. A liquid crystal mask the pixels of which have the same size can be used. In this case, the controller controls the liquid crystal mask such that a marking position of a block currently displayed on the liquid crystal mask overlaps a marking position of a block adjacent to the currently displayed block by a given length (L3, L4) of a portion corresponding to part of the outermost pixels of the liquid crystal mask.

TECHNICAL FIELD

This invention relates to a liquid crystal laser marker using a liquidcrystal mask and a marking method using the same.

BACKGROUND ART

One of the widely used laser markers that provide a laser beam formarking characters or figures on workpieces, such as semiconductorpackages, is a so-called liquid crystal laser marker using a liquidcrystal mask. In the liquid crystal laser marker, a design of thecharacters or figures to be marked is converted to dot information,e.g., where "0" indicates an unmarking portion and "1" indicates amarking portion, and is displayed on the liquid crystal mask having agiven number of pixels in accordance with the dot information. Then alaser beam is directed to be incident on the liquid crystal mask and istransmitted through the pixels, corresponding to the characters orfigures, to the surface of a workpiece so that the workpiece will bemarked with the transmitted laser beam. Therefore, the more the numberof pixels of the liquid crystal mask increases per unit area of theworkpiece, the more the characters or figures can be marked smoothlywith high resolution.

A conventional marking method for such a liquid crystal laser markerwill be described with respect to FIGS. 14 to 17.

FIG. 14 is a schematic diagram showing an exemplary structure of theliquid crystal laser marker. In FIG. 14, the laser oscillator 21 can bea YAG laser oscillator, the output of which is a pulse train driven by aQ switch. A first deflector 23X, 23Y conducts the laser beam from thelaser oscillator 21 to a liquid crystal mask 2 while deflecting it ingiven X and Y directions so that the liquid crystal mask 2 will beraster scanned. The first deflector comprises of an X-directionaldeflector or polygonal mirror 23X and a Y-directional deflector orgalvanometer scanner 23Y, provided separately from each other. Suchscanning directions, i.e., the X-axis scanned by rotating the polygonalmirror 23X and the Y-axis scanned by moving the galvanometer scanner23Y, intersect at right angles. The polygonal mirror 23X is rotatable inseveral constant speed rotation modes, and the rotation mode is selectedfor each workpiece to be marked. Each plane of the polygonal mirror 23Xcorresponds to one line in the X-direction on the liquid crystal mask 2.On the other hand, the galvanometer scanner 23Y is operable with givensteps of minute, equiangular deflections, and moves only by a minutedeflection angle and stops there as the light-receiving point of thelaser beam from the galvanometer scanner 23Y is changed from one planeto another by the rotation of the polygonal mirror 23X. Each of theminute deflection angles corresponds to one line feed in the Y-directionon the liquid crystal mask 2.

As shown in FIG. 15, the liquid crystal mask 2, called a transmissiondispersion type liquid crystal mask, can be a liquid crystal device inwhich a given number of liquid crystal elements are arranged in a dotmatrix. The liquid crystal elements constituting the liquid crystal mask2 have the same size. Further, electrode lines, not shown, are arrangedon both sides of the liquid crystal elements so as to be parallel oneach side and to perpendicularly intersect between both sides. Theelectrode lines apply a given voltage to certain or specific liquidcrystal elements to place them in a laser-beam transmission state. Theother liquid crystal elements to which no voltage is applied are in alaser-beam scattered state. The liquid crystal elements arranged in thedot matrix are used as the pixels 3 of a design to be marked. Each ofthe pixels 3 is converted to dot information "0" or "1", where "0"indicates an unmarking portion and "1" indicates a marking portion. Thegiven voltage is applied to the pixels 3 corresponding to the portionsto be marked such dot information is displayed on the liquid crystalmask 2, so that the laser beam will be transmitted therethrough, thusmarking a workpiece with the transmitted laser beam. As discussed above,the liquid crystal mask 2 serves as a light shutter for transmitting orintercepting a light beam in response to an external signal.

A second deflector 27X, 27Y conducts the laser beam from the liquidcrystal mask 2 to a marked surface of a workpiece 30 and deflects it ingiven X and Y directions on the workpiece 30. The second deflectorcomprises an X-directional deflector or galvanometer scanner 27X and aY-directional deflector or lens system 27Y, provided separately fromeach other. Such directions, i.e., the X-axis in which the laser beam isdeflected by rotating the galvanometer scanner 27X and the Y-axis inwhich the laser beam is deflected by moving the lens 27Y in parallel tothe workpiece 30, intersect at right angles. The laser beam transmittedthrough the liquid crystal mask 2 is conducted to the workpiece 30 viathe galvanometer scanner 27X for X-directional deflection, an objectlens 28, and the lens 27Y for Y-directional deflection. Thus, the designdisplayed on the liquid crystal mask 2 is marked on the workpiece 30.The lens 27Y for Y-directional deflection is set in a hole of a table 36and is moved along with the table 36 in parallel to the surface of theworkpiece 30. The table 36 is coupled through a link mechanism to anoutput shaft of a drive unit 35, such as an AC motor, and is driven bythe drive unit 35 to move in parallel. The second deflector 27X, 27Y isin a stopped state until all of the pixels corresponding to the designon the liquid crystal mask 2 are raster scanned so that the laser beamtransmitted through the liquid crystal mask 2 can be directed to amarking area of the design.

Further, optical systems for gathering or condensing laser light arearranged within incidence paths to the first deflector 23X, 23Y and tothe second deflector 27X, 27Y, respectively. Such condenser opticalsystems are effective in condensing incident light when the beam haslarge diameter or deflection angle, thus reducing any occurrence ofmodification of the mark or dispersion or loss of laser light.

The condenser optical system for the first deflector 23X, 23Y isconstituted of a relay lens (e.g., beam splitter) 22 between the laseroscillator 21 and the galvanometer scanner 23Y, and a relay lens 24between the galvanometer scanner 23Y and the polygonal mirror 23X. Therelay lens 22 gathers or condenses the laser beam from the laseroscillator 21 onto the reflection plane of the galvanometer scanner 23Y,while the relay lens 24 gathers the deflected beam from the galvanometerscanner 23Y to a point on each plane of the polygonal mirror 23X. Thelaser beam from the polygonal mirror 23X to the liquid crystal mask 2 isthus made uniform for raster scanning.

The condenser optical system for the second deflector 27X, 27Y isconstituted by a relay lens (e.g., field lens) 25, arranged between thepolygonal mirror 23X and the galvanometer scanner 27X and close to theliquid crystal mask 2. The relay lens 25 alters the raster-scanned beamfrom the polygonal mirror 23X into parallel rays, and the galvanometerscanner 27X reflects the parallel rays. The relay lens 25 can bearranged on the incidence side of the liquid crystal mask 2, as shown inFIG. 14, or on the emission side or on both sides.

A controller 11 is such a computer system that mainly has amicrocomputer. The controller 11 is connected to the liquid crystal mask2, the drive unit 32 for the polygonal mirror 23X, the Q switch for thelaser oscillator 21, the drive unit 31 for the galvanometer scanner 23Y,the drive unit 34 for the galvanometer scanner 27X, and the drive unit35 for the lens 27Y, respectively. These elements or units arecontrolled by the controller 11.

FIG. 16 shows an exemplary design to be marked. When the design islarger than the number of pixels on the liquid crystal mask 2, markingwith one emission of the laser beam causes lowered resolution of themarked design, and hence rough characters or lines. In such a case, itis necessary to use the liquid crystal mask 2 several times for areduced design area (hereinafter, referred to as a block) to be markedwith one emission of the laser beam. For example, the overall design isdivided into two blocks 1 in lateral and vertical directions,respectively. Then a design portion corresponding to each respectivedivided block 1 is displayed on the liquid crystal mask 2, and is markedin position on the workpiece 30 one by one. After all of the individualblocks 1 have been marked, the blocks 1 are synthesized and the overalldesign is completely marked.

Stated more particularly, a block 1 is first selected from among all ofthe blocks 1 during the condition that the oscillating power of thelaser oscillator 21 is turned off by the Q switch. The design portion ofthe selected block 1 is displayed on the liquid crystal mask 2 as dotinformation "0" and "1". The first deflector 23X, 23Y is driven to moveto and stop at a position from which the raster scanning is started,while the second deflector 27X and 27Y is driven to move to and stop ina marking area corresponding to the marking position of the selectedblock 1. Then the laser oscillator 21 is turned ON by the Q switch tooutput pulses, and the first deflector 23X, 23Y is driven so that thedesign portion on the liquid crystal mask 2 will be raster scanned. Theselected block 1 is thus marked on the workpiece 30.

The above process is performed for the other blocks 1 sequentially andrepeatedly until the overall design is marked on the workpiece 30.

In the conventional art, a design portion of each block 1 is displayedon the liquid crystal mask 2 and is marked on the workpiece 30 asdiscussed above.

However, with such a conventional technique, a character or figure maybe divided into different blocks 1. In this case, the identicalcharacter or figure must be marked on the workpiece 30 several times.

It is therefore necessary to coincide the joints of adjacent blocks witheach other when marking the identical character or figure several times,but such an adjustment is difficult because of various factors, such asa play of the second deflector 27X and 27Y, the changes in the positionof optical elements, and a change of a control signal due to externalnoise, and a gap may occur in the joint between adjacent blocks. In FIG.16, a character "I" is divided into two parts. FIG. 17A shows a statewhere the divided character "I" has been marked normally, whereas FIG.17B shows the character "I" marked in the condition that a gap occurs inthe joint between the two blocks 1. As shown in FIG. 17B, the gapbetween the blocks 1 causes a portion in which no laser beam isirradiated, and hence a break in the character or figure. As a result, aproblem arises in that the visibility of the marked design is lowered.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblem, and an object thereof is to provide a liquid crystal mask, aliquid crystal laser marker, and a marking method using the same, whichprevent occurrence of a gap in a joint between adjacent blocks when adesign is marked in several blocks.

A first aspect of the present invention provides a liquid crystal maskwith a plurality of pixels, mounted in a liquid crystal laser marker formaking the pixels display a design to be marked on workpieces and fortransmitting a laser beam through the pixels to a workpiece so that thedesign displayed on the pixels will be marked on the workpiece, whereinthe liquid crystal mask is a liquid crystal device in which the pixelsat all or part of the outermost sides, out of all of the pixels, have asize which is different from that of the inner pixels.

A fourth aspect of the present invention provides a liquid crystal lasermarker for making a liquid crystal mask, with a plurality of pixels,display a design to be marked on workpieces and for transmitting a laserbeam through the liquid crystal mask to a workpiece so that the designwill be marked on the workpiece, wherein the pixels at all or part ofthe outermost sides have a size which is different from that of theinner pixels.

A tenth aspect of the present invention provides a marking method formaking a liquid crystal mask, with a plurality of pixels, display adesign to be marked on workpieces and for transmitting a laser beamthrough the liquid crystal mask to a workpiece so that the design willbe marked on the workpiece, wherein the pixels at all or part of theoutermost sides or at least one side of the liquid crystal mask have asize which is different from that of the inner pixels such that thedesign is marked without distortion of the outermost optics.

According to the first, fourth and tenth aspects of the presentinvention, the liquid crystal mask is a liquid crystal device in whichthe outer pixels, at all or part of the outermost sides, have a sizewhich is different from that of the inner pixels. When a design isdivided into several blocks and each of the blocks is marked via theliquid crystal mask, the adjacent blocks are overlapped in a portionwhere the different sized outer pixels are lined up. The size of suchouter pixels can be set by taking into account various factors, such asthe play of the second deflector, the changes in position of opticalelements, and a change of a control signal due to external noise. Thismakes it possible to prevent an occurrence of a gap in the joint betweenadjacent blocks, and hence an occurrence of unmarked portions.Accordingly, high visibility of the marked design can be obtained evenif the design is marked in several blocks.

A fifth aspect of the present invention provides a liquid crystal lasermarker based on the fourth aspect of the present invention, wherein theliquid crystal laser marker further includes a controller, so that whena design is divided into several blocks and one of the blocks isdisplayed on the liquid crystal mask, the controller controls the liquidcrystal mask such that a marking position of the block, currentlydisplayed on the liquid crystal mask, overlaps a marking position of ablock adjacent to the currently displayed block by a given length of aportion where the outermost pixels have a size which is different fromthat of the inner pixels of the liquid crystal mask.

An eleventh aspect of the present invention provides a marking methodbased on the tenth aspect of the present invention, wherein when adesign is divided into several blocks and one of the blocks is displayedon the liquid crystal mask, a marking position of the block, currentlydisplayed on the liquid crystal mask, is overlapped with a markingposition of a block adjacent to the currently displayed block by a givenlength of a portion where the outermost pixels have a size which isdifferent from that of the inner pixels of the liquid crystal mask.

According to the fifth and eleventh aspects of the present invention,the controller divides a design into several blocks and controls theliquid crystal mask such that a marking position of a block, currentlydisplayed on the liquid crystal mask, overlaps a marking position of ablock adjacent to the currently displayed block by a given length of aportion where the outermost pixels have a size which is different fromthat of the inner pixels of the liquid crystal mask. The overlap amountof the pixels can be set by taking into account the non-uniformity ofpositioning accuracy of the liquid crystal mask and the laser beam. Thismakes it possible to prevent an occurrence of a gap in the joint betweenadjacent blocks, and hence an occurrence of unmarked portions.Accordingly, high visibility of the marked design can be obtained evenif the design is marked in several blocks. This enables the design to bemarked in a larger number of blocks, and it is easier to respond torequirements for high resolution (smoothness of the mark). Further,since the greater the number of blocks the smaller the size of theliquid crystal mask can be, the size and the cost of the laser markercan also be reduced.

A second aspect of the present invention provides a liquid crystal maskbased on the first aspect of the present invention, wherein the pixelsat two outermost sides opposite to each other laterally or verticallyare different from the inner pixels at least in either vertical size orlateral size.

A sixth aspect of the present invention provides a liquid crystal lasermarker based on the fifth aspect of the present invention, wherein theliquid crystal mask is such that the pixels at the outermost sides,opposite to each other vertically or laterally, are different from theinner pixels at least in either vertical size or lateral size, and whena design is divided into several blocks and one of the blocks isdisplayed on the liquid crystal mask, the controller controls the liquidcrystal mask such that a marking position of the block, currentlydisplayed on the liquid crystal mask, overlaps a marking position of ablock adjacent to the currently displayed block by a given length of aportion where the pixels at one of the opposite sides have a size whichis different from that of the inner pixels of the liquid crystal mask.

A twelfth aspect of the present invention provides a marking method formaking a liquid crystal mask with a plurality of pixels display a designto be marked on workpieces and for transmitting a laser beam through theliquid crystal mask to a workpiece so that the design will be marked onthe workpiece, wherein the pixels at the outermost sides, opposite toeach other vertically or laterally, are different from the inner pixelsat least in either vertical size or lateral size, and when a design isdivided into several blocks and one of the blocks is displayed on theliquid crystal mask, a marking position of the block, currentlydisplayed on the liquid crystal mask, is overlapped with a markingposition of a block adjacent to the currently displayed block by a givenlength of a portion where the pixels at one of the outermost sides,opposite to each other vertically or laterally, have a size which isdifferent from that of the inner pixels of the liquid crystal mask.

According to the second, sixth and twelfth aspects of the presentinvention, the liquid crystal mask is such that the pixels at theoutermost sides, opposite to each other vertically or laterally, aredifferent from the inner pixels at least in either vertical size orlateral size, and the controller controls the liquid crystal mask suchthat a marking position of a block, currently displayed on the liquidcrystal mask, overlaps a marking position of a block adjacent to thecurrently displayed block by a given length of a portion where theoutermost pixels have a size which is different from that of the innerpixels. Therefore, high visibility can be obtained even if the design ismarked in a number of blocks. This enables the design to be marked in alarger number of blocks. Further, when a design, which extends in onedirection, is divided in its longitudinal direction, the overall size ofthe marked design is not changed from that of the original, thus markingthe design with a high tolerance.

A third aspect of the present invention provides a liquid crystal maskbased on the first aspect of the present invention, wherein the pixels,at either of the outermost sides opposite to each other vertically oreither of the outermost sides opposite to each other laterally, aredifferent from the inner pixels at least in either vertical size orlateral size.

A seventh aspect of the present invention provides a liquid crystallaser marker based on the fifth aspect of the present invention, whereinthe liquid crystal mask is such that the pixels, at either of theoutermost sides opposite to each other vertically or either of theoutermost sides opposite to each other laterally, are different from theinner pixels at least in either vertical size or lateral size, and whena design is divided into several blocks and one of the blocks isdisplayed on the liquid crystal mask, the controller controls the liquidcrystal mask such that a marking position of the block, currentlydisplayed on the liquid crystal mask, overlaps a marking position of ablock adjacent to the currently displayed block by a given length of aportion where the pixels at either of the opposite sides have a sizewhich is different from that of the inner pixels of the liquid crystalmask.

A thirteenth aspect of the present invention provides a marking methodfor making a liquid crystal mask with a plurality of pixels display adesign to be marked on workpieces and for transmitting a laser beamthrough the liquid crystal mask to a workpiece so that the design willbe marked on the workpiece, wherein the pixels, at either of theoutermost sides opposite to each other vertically or either of theoutermost sides opposite to each other laterally, are different from theinner pixels at least in either vertical size or lateral size, and whena design is divided into several blocks and one of the blocks isdisplayed on the liquid crystal mask, a marking position of the block,currently displayed on the liquid crystal mask, is overlapped with amarking position of a block adjacent to the currently displayed block bya given length of a portion where the outermost pixels at either of theopposite sides have a size which is different from that of the innerpixels of the liquid crystal mask.

According to the third, seventh and thirteenth aspects of the presentinvention, the liquid crystal mask is such that the pixels, at either ofthe outermost sides opposite to each other vertically or either of theoutermost sides opposite to each other laterally, are different from theinner pixels at least in either vertical size or lateral size, and thecontroller controls the liquid crystal mask such that a marking positionof a block currently displayed on the liquid crystal mask overlaps amarking position of a block adjacent to the currently displayed block bya given length of a portion where the outermost pixels have a size whichis different from that of the inner pixels. Therefore, high visibilitycan be obtained even if the design is marked in several blocks. Thisenables the design to be marked in a larger number of blocks. Further,when a design, which extends in one direction, is divided in itslongitudinal direction, the overall size of the marked design is notchanged from that of the original, thus marking the design with a hightolerance.

An eighth aspect of the present invention provides a liquid crystallaser marker for making a liquid crystal mask with a plurality of pixelsdisplay a design to be marked on workpieces and for transmitting a laserbeam through the liquid crystal mask to a workpiece so that the designwill be marked on the workpiece, wherein the liquid crystal laser markerfurther includes a controller, so that when a design is divided intoseveral blocks and one of the blocks is displayed on the liquid crystalmask, the controller controls the liquid crystal mask such that amarking position of the block, currently displayed on the liquid crystalmask, overlaps a marking position of a block adjacent to the currentlydisplayed block by a given length of a portion corresponding to part ofthe outermost pixels of the liquid crystal mask.

A fourteenth aspect of the present invention provides a marking methodfor making a liquid crystal mask with a plurality of pixels display adesign to be marked on workpieces and for transmitting a laser beamthrough the liquid crystal mask to a workpiece so that the design willbe marked on the workpiece, wherein when a design is divided intoseveral blocks and one of the blocks is displayed on the liquid crystalmask, a marking position of the block currently displayed on the liquidcrystal mask is overlapped with a marking position of a block adjacentto the currently displayed block by a given length of a portioncorresponding to part of the outermost pixels of the liquid crystalmask.

According to the eighth and fourteenth aspects of the present invention,the liquid crystal mask is controlled by the controller such that amarking position of a block currently displayed on the liquid crystalmask overlaps a marking position of a block adjacent to the currentlydisplayed block by a given length of a portion corresponding to part ofthe outermost pixels at either of the opposite sides. The overlap amountcan be set by taking into account various factors, such as the play ofthe second deflector 27X and 27Y, the changes in position of opticalelements, and a change of a control signal due to external noise. Thismakes it possible to prevent an occurrence of a gap in the joint betweenadjacent blocks, and hence an occurrence of unmarked portions even whenall the pixels of the liquid crystal mask have the same size.Accordingly, high visibility of the marked design can be obtained evenif the design is marked in a number of blocks, and it is easier torespond to requirements for high resolution (smoothness of the mark).Further, since the greater the number of blocks the smaller the size ofthe liquid crystal mask can be, the size and the cost of the lasermarker can also be reduced.

A ninth aspect of the present invention provides a liquid crystal maskbased on the eighth aspect of the present invention, wherein the givenlength for overlapping the marking positions of adjacent blocks,displayed one at a time on the liquid crystal mask, has units of dotstarting from the outermost pixel.

A fifteenth aspect of the present invention provides a marking methodbased on the fourteenth aspect of the present invention, wherein thegiven length for overlapping the marking positions of adjacent blocks,displayed one at a time on the liquid crystal mask, has units of dotstarting from the outermost pixel.

According to the ninth and fifteenth aspects of the present invention, apart of the outermost pixels of the liquid crystal mask is overlapped indot unit. Therefore, high visibility of the marked design can beobtained even if the design is marked in a number of blocks. Thisenables the design to be marked in a larger number of blocks, and it iseasier to respond to requirements for high resolution (smoothness of themark). Further, since the greater the number of blocks the smaller thesize of the liquid crystal mask can be, the size and the cost of thelaser marker can be also reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a liquid crystal mask according to a firstembodiment of the present invention.

FIGS. 2 and 3 show other examples of liquid crystal masks according tothe first embodiment of the present invention.

FIG. 4 shows an example of a method for dividing a design into in thefirst embodiment of the present invention.

FIG. 5 shows another example of a method for dividing a design intoblocks in the first embodiment of the present invention.

FIG. 6 shows an example of marking positions in the first embodiment ofthe present invention.

FIG. 7 shows another example of marking positions in the fir embodimentof the present invention.

FIG. 8 shows an example of an overlapping portion between adjacentblocks marked by the liquid crystal mask according to the firstembodiment of the present invention.

FIGS. 9 and 10 each show another example of marking positions in thefirst embodiment of the present invention.

FIG. 11 shows another example of an overlapping portion between adjacentblocks marked by the liquid crystal mask according to the firstembodiment of the present invention.

FIG. 12 shows an example of a method for dividing a design into blocksand for marking positions in a second embodiment of the presentinvention.

FIG. 13 shows another example of a method for dividing a design intoblocks and for marking positions in the second embodiment of the presentinvention.

FIG. 14 is a perspective view showing a general structure of anexemplary laser marker.

FIG. 15 is a schematic diagram showing a liquid crystal mask.

FIG. 16 is a schematic diagram showing an example of a method dividing adesign into blocks in the conventional art.

FIG. 17A and 17B are explanatory drawings each showing a joint betweenblocks in the conventional art.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 through 11, a liquid crystal mask, a liquid crystallaser marker, and a marking method using the same according to a firstembodiment of the present invention will be described. In theembodiment, liquid crystal masks 2a, 2b or 2c are used, where all orpart of the outermost pixels have a size which is larger than that ofthe other pixels of the liquid crystal mask 2. The liquid crystal lasermarker according to the embodiment has the same structure as that ofFIG. 14.

FIGS. 1 to 3 shows the liquid crystal masks 2a, 2b, and 2c used in theembodiment, respectively. Each of the liquid crystal masks is a liquidcrystal device serving as a light shutter for transmitting orintercepting a light beam in response to an external signal.

FIG. 1 shows the liquid crystal mask 2a having pixels, only at one side,out of all of the outermost sides of the liquid crystal mask, which aredifferent in size from that of the other pixels. FIG. 2 shows the liquidcrystal mask 2b having pixels only at one side in each of two pairs ofopposite sides, out of all of the outermost sides of the liquid crystalmask, which are different in size from that of the other pixels.

FIG. 3 shows the liquid crystal mask 2c having pixels at all of theoutermost sides of the liquid crystal mask which are different in sizefrom that of the inner pixels. In these cases, the size of the pixelsarranged at the corresponding side or sides is set larger than that ofthe other pixels. The liquid crystal masks 2a, 2b, and 2c have avertical length A and a horizontal length B. The pixels, with a sizelarger in the vertical direction, have a vertical length E1 which islonger by a given length L1 than a vertical length E of the otherpixels. The pixels, with the size larger in the lateral direction, havea horizontal length F1 which is longer by a given length L₂ than ahorizontal length F of the other pixels. The lengths L₁ and L₂ can beset to prevent an occurrence of a gap in each joint by taking intoaccount the maximum gap in the joint caused by various factors, such asthe play of the second deflector 27X and 27Y, the changes in position ofoptical elements, and a change of a control signal due to externalnoise.

On the other hand, a design to be marked is divided into several blocks1 without overlapping each other. FIG. 4 shows an example of a designwhich is divided into three blocks 1 in the longitudinal direction. FIG.5 shows an example of a design divided into three blocks 1 in thevertical direction and two blocks 1 in the lateral direction. Each block1 is set such that characters or figures of the design can be markedsmoothly with the resolution (the number of pixels) of the liquidcrystal mask 2 used. It should be noted here that the design needs to bedivided into blocks such that at each joint the adjacent blocks 1 neveroverlap each other.

Next, operation in the first embodiment will be described.

FIG. 6 shows marking positions when the design is marked through theliquid crystal mask 2a having larger-sized pixels only at either of twosides which are opposite to each other vertically or laterally as shownin FIG. 1, in which the design is divided in the longitudinal directionas in FIG. 4. The controller 11 makes the liquid crystal mask 2a displayeach block 1, resulting from division in the longitudinal direction, andinstructs the drive units 32 and 31 for the first deflector 23X and 23Yto output a laser beam so that the liquid crystal mask 2a will be rasterscanned with the laser beam. Then the second deflector 27X and 27Y ispositioned by the controller 11 such that the marking position faces amarking area corresponding to the block 1 currently displayed. Themarking position is determined such that the adjacent blocks 1 overlapeach other in the vertical direction by a portion corresponding to thegiven length L1 of the liquid crystal mask 2a.

FIG. 7 shows marking positions when the design is marked through theliquid crystal mask 2b having larger-sized pixels only at one side ofeach of two pairs of the opposite sides as shown in FIG. 2, in which thedesign is divided in the vertical and lateral directions as in FIG. 5.The controller 11 makes the liquid crystal mask 2b display each block 1,resulting from division in the vertical and lateral directions, andinstructs the drive units 32 and 31 for the first deflector 23X and 23Yto output a laser beam so that the liquid crystal mask 2b will be rasterscanned with the laser beam. Then the second deflector 27X and 27Y ispositioned by the controller 11 such that the marking position faces amarking area corresponding to the block 1 currently displayed. Themarking position is determined such that the adjacent blocks 1 overlapeach other in the vertical direction by a portion corresponding to thegiven length L1 of the liquid crystal mask 2b and in the lateraldirection by a portion corresponding to the given length L₂ of theliquid crystal mask 2b.

Such an overlapping portion between adjacent blocks 1 will be describedin detail below with reference to FIG. 8. FIG. 8 shows an overlappingportion between adjacent blocks 1 displayed one at a time on the liquidcrystal mask 2a or 2b. In the case where the liquid crystal mask 2a isused to overlap the adjacent blocks 1 in the vertical direction, themarking position is determined such that a portion corresponding to thegiven length L1, at the lower end and within the length E1 of thelowermost row of pixels of the liquid crystal mask on which a block 1 isdisplayed, is overlapped with part of the length E of the uppermost rowof pixels of the liquid crystal mask on which a block 1 adjacent to andbelow the above block 1 is displayed. Similarly, in the case the liquidcrystal mask 2b is used to overlap the adjacent blocks 1 in the lateraldirection, the marking position is determined such that a portioncorresponding to the given length L₂ at the right end and within thelength F1 of the rightmost row of pixels of the liquid crystal mask onwhich a block 1 is displayed is overlapped with part of the length F ofthe leftmost row of pixels of the liquid crystal mask on which a block 1adjacent to and to the right of the above block 1 is displayed.

On the other hand, in the case of the liquid crystal mask 2c havinglarger-sized pixels at two pairs of opposite sides as shown in FIG. 3,the marking position is determined as in FIG. 9 or 10. FIG. 9 showsmarking positions when the design is divided in the longitudinalpositions when the design is divided in direction as in FIG. 4. FIG. 10shows marking positions when the design is divided in the vertical andlateral directions as in FIG. 5. When the design is divided in thelongitudinal direction, there can be used a liquid crystal mask havinglarger-sized pixels at the sides opposite to each other eithervertically or laterally. The controller 11 makes the liquid crystal mask2c display each block 1 of a design which is divided in the longitudinaldirection or of a design which is divided in the vertical and lateraldirections, and provides a laser beam for raster scanning of the liquidcrystal mask 2c with the first deflector 23X and 23Y. Then the seconddeflector 27X and 27Y is positioned under control such that the markingposition faces a marking area corresponding to the block 1 currentlydisplayed. The marking position is determined such that the adjacentblocks 1 overlap each other in the vertical direction by a portioncorresponding to a length 2uL₁ that is twice as long as the given lengthL₁ of the liquid crystal mask 2c, and in the lateral direction by aportion corresponding to a length 2uL₂ that is twice as long as thegiven length L₂ of the liquid crystal mask 2c.

Such an overlapping portion between adjacent blocks 1 will be describedin detail below with reference to FIG. 11. FIG. 11 shows an overlappingportion between adjacent blocks 1 displayed one at a time on the liquidcrystal mask 2c. When the adjacent blocks 1 overlap each other in thevertical direction, the marking position is determined such that aportion corresponding to the length 2uL₁ at the lower end and within thelength E1 of the lowermost row of pixels of the liquid crystal mask onwhich a first block 1 is displayed is overlapped with the length 2uL₁ atthe upper end and within the length E1 of the uppermost row of pixels ofthe liquid crystal mask on which a block 1 adjacent to and below thefirst block 1 is displayed. Similarly, when the adjacent blocks 1overlap each other in the lateral direction, the marking position isdetermined such that a portion corresponding to the length 2uL₂ at theright end and within the length F₁ of the rightmost row of pixels of theliquid crystal mask on which a first block 1 is displayed is overlappedwith the length 2uL₂ at the left end of the leftmost row of pixels ofthe liquid crystal mask on which a block 1 adjacent to and to the rightof the first block 1 is displayed.

Although the above embodiment teaches that the vertical length E₁ of thepixels of all of the outermost pixels having a different size is setlonger by the given length L₁ than the vertical length E of the otherpixels, the present invention is not limited by the embodiment and itcan be set shorter than the length E, e.g., to a length equal to thegiven length L₁ (where L₁ <E). The liquid crystal mask can be such thatthe pixels having the length E₁ (longer than the length E by the givenlength L₁) are arranged at one of the opposite sides and the pixelshaving the length L₁ (where L₁ <E) is arranged at the other side. Evenin this case, the adjacent blocks 1 are overlapped in the same manner asin FIGS. 8 and 11. Stated more particularly, when the pixel size at oneof the opposite sides is different from that at the other side, i.e.,when the one is E₁ and the other is L₁, a portion corresponding to thegiven length L₁ of the pixel at one of the opposite sides of the liquidcrystal mask on which a block 1 is displayed is overlapped with theadjacent block 1.

Similarly, when the pixels at two pairs of opposite sides are differentin size from the other pixels, a portion corresponding to the length2uL₁ of the pixels at the opposite sides of the liquid crystal mask onwhich a block 1 is displayed is overlapped with the adjacent block 1.

Although the above embodiment also teaches that the horizontal length F₁of the pixels different in size is longer by the given length L₂ thanthe horizontal length F of the other pixels, the present invention isnot limited by the embodiment and it can be set shorter than the lengthF, e.g., to a length equal to the given length L₂ (where L₂ <F). Theliquid crystal mask can be such that the pixels having the length F₁(longer than the length F by the given length L₂) is arranged at one ofthe opposite sides and the pixels having the length L₂ (where L₂ <F) isarranged at the other side. Even in this case, the adjacent blocks 1 areoverlapped in the same manner as in FIGS. 8 and 11.

According to such structures of the liquid crystal masks, the adjacentblocks 1 are overlapped exactly in the joint even when an inconvenientthing occurs, such as the play of the second deflector 27X and 27Y,changes in the position of optical elements, and a change of a controlsignal due to external noise. This makes it possible to eliminate aportion in which no laser beam is irradiated, and hence to obtain highvisibility of the overall design. Further, when a design is divided intoseveral blocks in its longitudinal direction, the longitudinal size ofthe marked figure can be the same as that of the original design, sothat a yield of marking in the laser marker increases, thus improvingits productivity.

Even when the design is divided into several blocks 1 withoutoverlapping each other, since an overlapping portion is provided inadvance in a marking area, it is not necessary to increase the accuracywith which the marking position of each block is controlled as long asthe overlapping portion is within the tolerance. Further, since no gapoccurs in the joint between adjacent blocks, the design can be marked ina larger number of blocks. It is therefore possible to make each blocksmaller when high resolution (smoothness of the mark) is required, andhence easier to respond to requirements for high resolution.Furthermore, the size of a liquid crystal mask to be used can beminimized by reducing the number of pixels of the liquid crystal mask,thereby reducing the size and the cost of the laser marker.

A second embodiment will be described next. In this embodiment, a liquidcrystal mask 2 has pixels 3 of an identical size as shown in FIG. 15.The liquid crystal laser marker according to this embodiment has thesame structure as that of FIG. 14.

FIGS. 12 and 13 each show an example of a design divided into severalblocks 1 in the longitudinal direction or in the vertical and lateraldirections. In such examples, overlapping portions of given lengths L₃and L₄ are provided in a vertical joint or a horizontal joint betweenadjacent blocks 1, respectively. The given lengths L₃ and L₄ can be setto prevent occurrence of a gap in each joint by taking into account themaximum gap in the joint caused by various factors, such as the play ofthe second deflector 27X and 27Y, the changes in the position of opticalelements, and a change of a control signal due to external noise. Eachblock 1 is set such that the characters or figures of the design can bemarked smoothly with the resolution (the number of pixels) of the liquidcrystal mask 2 used.

Next, operation in the second embodiment will be described.

When a design is divided in the longitudinal direction as shown in FIG.12, the marking positions are controlled in the following manner. Thecontroller 11 makes the liquid crystal mask 2 display each block 1,representing divisions in the longitudinal direction, and provides alaser beam for raster scanning of the liquid crystal mask 2 with thefirst deflector 23X and 23Y. Then the second deflector 27X and 27Y ispositioned by the controller 11 such that the current marking positionfaces a marking area corresponding to the block 1 currently displayed.The marking position is determined such that the adjacent blocks 1overlap each other in the vertical direction by the given length L₃.

As shown in FIG. 13, when a design is divided in the vertical andlateral directions, the controller 11 makes the liquid crystal mask 2sequentially display each block 1, and provides a laser beam for theraster scanning of the liquid crystal mask 2 with the first deflector23X and 23Y. Then the second deflector 27X and 27Y is positioned by thecontroller 11 such that the current marking position faces a markingarea corresponding to the block 1 currently displayed. The markingposition is determined such that the adjacent blocks 1 overlap eachother in the vertical direction by the given length L₃ and in thelateral direction by the given length L₄.

The lengths L₃ and L₄ of overlapping portions between adjacent blocks 1can be set to a size in pixel unit (dot unit) or to a length shorterthan the size of one pixel.

According to such structures, the adjacent blocks 1 are overlappedexactly in the joint even when an inconvenient thing occurs, such as theplay of the second deflector 27X and 27Y, the changes in the position ofoptical elements, and a change of a control signal due to externalnoise. This makes it possible to eliminate a portion in which no laserbeam is irradiated, and hence to obtain high visibility of the overalldesign. Further, when a design is divided into several blocks in itslongitudinal direction, the longitudinal size of the marked figure canbe the same as that of the original design, so that a yield of markingin the laser marker increases, thus improving its productivity.

Since an overlapping portion between adjacent blocks is provided inadvance, it is not necessary to increase the accuracy with which themarking position of each block is controlled as long as the overlappingportion is within the tolerance. Further, since no gap occurs in thejoint between adjacent blocks, the design can be marked in a largernumber of blocks. It is therefore possible to make each block smallerwhen high resolution (smoothness of the mark) is required, and henceeasier to respond to requirements for high resolution. Furthermore, thesize of a liquid crystal mask to be used can be minimized by reducingthe number of pixels of the liquid crystal mask, thereby reducing thesize and the cost of the laser marker.

INDUSTRIAL APPLICABILITY

According to the present invention, no gap occurs in the joint betweenadjacent blocks when a design is marked in several blocks. Therefore,the present invention is effectively applied to a liquid crystal mask, aliquid crystal laser marker, and a marking method using the same, inwhich high visibility of the marked design is obtained without any breakin the character or figure.

What is claimed is:
 1. A liquid crystal mask with a plurality of pixels,said liquid crystal mask being suitable for mounting in a liquid crystallaser marker for making the pixels display a design to be marked onworkpieces and for transmitting a laser beam through the pixels to aworkpiece so that the design displayed on the pixels will be marked onthe workpiece, said liquid crystal mask being a liquid crystal devicehaving a plurality of outer pixels arranged along outermost sides ofsaid liquid crystal device and a plurality of inner pixels arrangedinwardly of said outer pixels, in which the outer pixels of at least aportion of the outermost sides have a size which is different from thatof the inner pixels.
 2. A liquid crystal mask according to claim 1,wherein the outer pixels at two outermost sides, which are opposite toeach other laterally, are different from the inner pixels at least inlateral size.
 3. A liquid crystal mask according to claim 1, wherein theouter pixels at two outermost sides, which are opposite to each othereither vertically, are different from the inner pixels at least invertical size.
 4. A liquid crystal mask according to claim 1, whereinthe pixels at either one of the outermost sides which are opposite toeach other vertically are different from the inner pixels at least invertical size.
 5. A liquid crystal mask according to claim 1, whereinthe pixels at either one of the outermost sides which are opposite toeach other laterally are different from the inner pixels at least inlateral size.
 6. A liquid crystal laser marker comprising:a liquidcrystal mask having a plurality of outer pixels arranged along outermostsides of said liquid crystal mask and a plurality of inner pixelsarranged inwardly of said outer pixels, in which the outer pixels of atleast a portion of the outermost sides have a size which is differentfrom that of the inner pixels; whereby said liquid crystal laser markercan display on said liquid crystal mask a design to be marked onworkpieces and transmit a laser beam through said liquid crystal mask toa workpiece so that the design will be marked on the workpiece.
 7. Aliquid crystal laser marker in accordance with claim 6, furthercomprising a controller, so that when a design is divided into severalblocks and one of the blocks is displayed on said liquid crystal mask,said controller controls said liquid crystal mask such that a markingposition of a block currently displayed on said liquid crystal maskoverlaps a marking position of a block adjacent to the currentlydisplayed block by a given length of a portion of the outer pixelshaving a size which is different from that of the inner pixels of saidliquid crystal mask.
 8. A liquid crystal laser marker in accordance withclaim 7, wherein said liquid crystal mask is such that the outer pixels,at the outermost sides which are opposite to each other vertically orlaterally, are different from the inner pixels in at least one ofvertical size and lateral size, and when a design is divided intoseveral blocks and one of the blocks is displayed on said liquid crystalmask, the controller controls said liquid crystal mask such that amarking position of a block currently displayed on said liquid crystalmask overlaps a marking position of a block adjacent to the currentlydisplayed block by a given length of a portion where the outer pixels,at one of the opposite outermost sides, have a size which is differentfrom that of the inner pixels of said liquid crystal mask.
 9. A liquidcrystal laser marker according to claim 7, wherein said liquid crystalmask is such that the outer pixels, at either of the outermost sideswhich are opposite to each other vertically or at either of theoutermost sides which are opposite to each other laterally, aredifferent from the inner pixels at least in either vertical size orlateral size, and when a design is divided into several blocks and oneof the blocks is displayed on said liquid crystal mask, the controllercontrols said liquid crystal mask such that a marking position of ablock currently displayed on said liquid crystal mask overlaps a markingposition of a block which is adjacent to the currently displayed blockby a given length of a portion where the outer pixels at either of theopposite sides have a size which is different from that of the innerpixels of said liquid crystal mask.
 10. A liquid crystal laser markercomprising:a liquid crystal mask having a plurality of outer pixelsarranged along outermost sides of said liquid crystal mask and aplurality of inner pixels arranged inwardly of said outer pixels; and acontroller, for displaying on said liquid crystal mask a design to bemarked on workpieces and for transmitting a laser beam through saidliquid crystal mask to a workpiece so that the design will be marked onthe workpiece, so that when a design is divided into several blocks andone of the blocks is displayed on said liquid crystal mask, saidcontroller controls said liquid crystal mask such that a markingposition of a block currently displayed on said liquid crystal maskoverlaps a marking position of a block adjacent to the currentlydisplayed block by a given length of a portion corresponding to part ofthe outer pixels of said liquid crystal mask.
 11. A liquid crystal lasermarker in accordance with claim 10, wherein the given length has unitsof dot starting from an outermost pixel.
 12. A marking method comprisingthe steps of:making a liquid crystal mask display a design to be markedon workpieces, said liquid crystal mask having a plurality of outerpixels arranged along outermost sides of said liquid crystal mask and aplurality of inner pixels arranged inwardly of said outer pixels,wherein in at least a portion of the outermost sides the outer pixelshave a size which is different from that of the inner pixels; andtransmitting a laser beam through the liquid crystal mask to a workpieceso that the design will be marked on the workpiece without distortion ofoutermost optics.
 13. A marking method in accordance with claim 12,further comprising the steps of:dividing a design into several blocks;displaying the blocks one by one on said liquid crystal mask;overlapping a marking position of a block currently displayed on saidliquid crystal mask with a marking position of a block which is adjacentto the currently displayed block by a given length of a portion wherethe outer pixels have a size which is different from that of the innerpixels.
 14. A marking method comprising:dividing into several blocks adesign to be marked on workpieces; providing a liquid crystal maskhaving a plurality of outer pixels arranged along outermost sides ofsaid liquid crystal mask and a plurality of inner pixels arrangedinwardly of said outer pixels, wherein the outer pixels of at least oneof the outermost sides, which are opposite to each other vertically orlaterally, are different from the inner pixels at least in eithervertical size or lateral size; making said liquid crystal mask displaysaid blocks one by one; and transmitting a laser beam through the liquidcrystal mask to a workpiece such that a marking position of a blockcurrently displayed on said liquid crystal mask is overlapped with amarking position of a block which is adjacent to the currently displayedblock by a given length of a portion where the outer pixels of said atleast one of the outermost sides which are opposite to each othervertically or laterally have a size which is different from that of theinner pixels, so that the design will be marked on the workpiece.
 15. Amarking method comprising the steps of:dividing into several blocks adesign to be marked on workpieces; providing a liquid crystal maskhaving a plurality of outer pixels arranged along outermost sides ofsaid liquid crystal mask and a plurality of inner pixels arrangedinwardly of said outer pixels, wherein the outer pixels, at either oneof the outermost sides which are opposite to each other vertically oreither of the outermost sides opposite to each other laterally, aredifferent from the inner pixels at least in either vertical size orlateral size, making said liquid crystal mask display said blocks one byone; and transmitting a laser beam through the liquid crystal mask to aworkpiece such that a marking position of a block currently displayed onsaid liquid crystal mask is overlapped with a marking position of ablock which is adjacent to the currently displayed block by a givenlength of a portion where the outer pixels at either of the oppositesides have a size which is different from that of the inner pixels, sothat the design will be marked on the workpiece.
 16. A marking methodcomprising the steps of:dividing into several blocks a design to bemarked on workpieces; providing a liquid crystal mask having a pluralityof outer pixels arranged along outermost sides of said liquid crystalmask and a plurality of inner pixels arranged inwardly of said outerpixels; making said liquid crystal mask display said blocks one by one;and transmitting a laser beam through the liquid crystal mask to aworkpiece such that a marking position of a block currently displayed onsaid liquid crystal mask is overlapped with a marking position of ablock which is adjacent to the currently displayed block by a givenlength of a portion corresponding to part of the outer pixels, so thatthe design will be marked on the workpiece.
 17. A marking method inaccordance with claim 16, wherein the given length has units of dotstarting from an outer pixel.